The working principle of a metal halogen lamp is that an arc is created between two electrodes enclosed in a burner glass tube (arc tube). The arc is generated by a mixture of suitable gases for emitting light. The burner glass tube is configured as compactly as possible, accommodating as large a part of the said gases as possible for consumption during operation. The burner glass tube is produced in elongated form with an electrode at each end and is expediently placed inside a closed space formed by a transparent glass body. In traditional metal halogen lamps, the burner contains a mixture of gases such as argon, mercury and metal halogens. The argon gas, through its ionization, enables the arc to be ignited when current is transported between the electrodes. The heat which is formed by the arc will then vaporize the mercury and the metal halogens. These vaporized metals produce light when the pressure is raised and the temperature rises in the burner.
During operation, in a first step, metal atoms move from the arc in the direction of the wall of the colder burner tube in which the halogens are found. On the wall, the metals and the halogens form stable molecules which do not corrode the burner tube. The formation takes place as a result of the formed vapour pressure and the increased temperature. When the metal halogens approach the arc again, the molecules will be broken up, whereby the halogens move away from the arc and the metal atoms remain in the arc and generate light. After this, the first step is started anew and the metal atoms move from the arc towards the halogens on the wall to form molecules, etc.
In certain cases, molecules of halogens and metal atoms are not formed, whereby the metal atoms will diffuse out through the wall of the burner tube. The fewer metal atoms there are in the burner tube, the worse is the production of light.
U.S. 2009/0153053 describes a metal halogen lamp having low mercury content in order to produce a more environmentally friendly lamp. The burner therefore comprises a content of zinc metal or zinc. The document describes that the length of the burner tube is directly proportional to the power consumption, whereby the length can be increased (make the burner tube longer and narrower) and thus the mercury vapour pressure reduced and the mercury component reduced. This gives an environmentally friendly lamp.
WO 2006/078632 A1 describes a metal halogen lamp of ceramic material with good light projection. The lamp which is described there is configured with a burner in three parts, having an intermediate tube part as well as two plug parts insertable in each end of the intermediate tube part and extending into the intermediate tube part by a distance substantially corresponding to the length of the electrode. Various types of gases are described to reduce erosion of the ceramic material in the tube part. At least two-fifths (40%) in total of the internal length of the burner tube are designated as a central region of the burner tube, which central region has a thinner wall thickness than the end portions of the burner tube with the insertable plug portions. Each thicker-walled end portion of the burner tube thus has a length of 30% or less of the total length of the burner tube. The burner tube likewise has an internally arranged step within the region of the transition between the intermediate tube part and the respective plug part.